The present invention relates to a method of transmitting another data by embedding it in image and/or voice data and to an apparatus for reproducing the transmitted data. Specifically, it relates to a data reproduction apparatus comprising LSI circuitry having the function of detecting embedded data.
Technologies for embedding another data in image, voice and text data are also called “data hiding”, “watermark”, and “electronic watermark” and have been investigated as a technology for embedding identification information or notes connected with these image, voice and text data.
These technologies have been recently been applied as a technology for embedding data for the protection of the copyright of these information to prevent illegal operation such as illegal reproduction. The technologies are described in “Nikkei Electronics” published by Nikkei BP Co. (pp. 149 to 162, Feb. 24, 1997).
If data to be embedded are deteriorated by processing operation such as the filtering and/or compression of original data, it loses the function of preventing illegal operation. Therefore, the method of embedding data is changed or data is embedded repeatedly so that the data still remain effective after these processes are carried out.
Various permissions concerning the limitation of reproduction are conceivable for original data. For example, original data can be reproduced, cannot be reproduced or can be reproduced only once in connection with copyright. It is now being considered that such control of reproduction is to be carried out by embedding data corresponding to these permissions and detecting it.
Heretofore, in the research and development of the function of detecting embedded data (to be referred to as “watermark detection function” hereinafter), special hardware and digital signal processors (DSP) have been used as watermark detection devices. The reason for this is that the data processing required for the implementation of a watermark detection device is complicated and high operation speed is required. As a result, the cost of a watermark detection device is significantly large compared with the cost of a system incorporating this device.
Owing to recent progress made in semiconductor technology, the performance-cost ratio of a high-speed arithmetic unit greatly improves. Considering that devices which carry out reproduction control are image/voice reproduction devices for domestic use such as DVD video players and that they are relatively inexpensive, there still remains such a problem that costs required for the addition of a watermark detection function cannot be negligible.
To solve the above problem, a watermark detection circuit must be made inexpensive by reducing its scale. Generally speaking, to cut the cost of a digital arithmetic unit while maintaining its certain functions, the following methods are effective:
(1) a portion where parallel processing is carried out is changed to perform a single processing in order to carry out serial processing, and
(2) arithmetic processing blocks such as a memory, adder and multiplier are made general-purpose blocks to be shared in each stage of arithmetic processing.
The downside of the above method is that the time required for processing is prolonged though they are effective in cost reduction.
The problem that the processing time required for watermark detection is prolonged will be described hereinafter, taking the case where DVD video reproduction which will be controlled shortly is carried out by a DVD player and a DVD-ROM drive.
Since DVD video data recorded on a DVD disk are MPEG2 formatted, the decoding of MPEG2 formatted data must be carried out to correctly reproduce original information. MPEG2 specifies the lowest data reproduction rate required for image and voice data at the time of decoding. When the transfer rate of data input into an MPEG2 decoder is lower than this rate, image and voice data cannot be reproduced correctly. Therefore, the MPEG2 data transfer rate has a lower limit.
Meanwhile, the data transfer rate which enables watermark detection is limited for the above reason. Therefore, the data transfer rate which enables watermark detection cannot be lower than the lower limit of the above MPEG2 data transfer rate.
In the DVD-ROM drive, how fast data can be transferred compared with the ordinary data transfer rate as an additional value of a product is considered to be the most important point. When the ordinary transfer rate specified by the standards is 1, DVD-ROM drives which can transfer data at a maximum data transfer rate 6 to 10 times higher than the ordinary transfer rate are already available on the market. The reduction of the data transfer rates of these products for watermark detection is not allowed from the viewpoint of product value.
Therefore, watermark detection from the output data of a DVD-ROM drive having a high data transfer rate involves more difficulties than in a DVD player in terms of data transfer rate which enables watermark detection.
As described above, to introduce reproduction control means making use of watermarks, such problems as costs required for the addition of a watermark detection function and processing speed which enables watermark detection must be solved at the same time. This is a big theme to be targeted.